1. Field of the Invention
The present invention generally relates to an apparatus and method useful for attaching one end of a coherent fiber-optic bundle to an electro-optical sensor. The present invention is particularly useful for accurately positioning the end of the fiber-optic bundle with respect to the face of the electro-optical sensor and retaining the bundle end permanently in place in the presence of vibrations, shocks and fluctuating temperatures and pressures. More particularly, the present invention provides a method of accurately positioning and attaching the end of the fiber-optic bundle to the electro-optical sensor by means of a rigid guide plate and transparent flexible attachment medium, avoiding damage to the sensor under adverse operating conditions.
2. Description of the Background
It is desirable to couple light signals to an electro-optical sensor through a coherent fiber-optic bundle as a substitute for a complex imaging system and in circumstances where the source of reflected or generated light is, for example, at a remote location from the sensor, at a location which is difficult of access for the sensor, or at a location where the environment would damage the sensor. The distal end of the bundle receives the light signals from the light source and the proximal end transmits the light signals to the sensor. The fiber-optic bundle is constructed such that a light signal incident upon the distal end of the bundle is delivered in the desired form to the bundle's proximal end surface. This surface is positioned to be mated with the light sensitive surface of the sensor and to deliver the signal to the desired area or areas of the sensor surface. To those skilled in the art it is obviously desirable that the relative positions of the bundle's proximal light-transmitting end and the light-sensitive surface of the sensor must be accurately maintained under operating conditions which may include shocks, vibrations and fluctuating temperatures and pressures, so that the light signal transmitted to the sensor consistently represents the light received by the distal end of the fiber-optic bundle. It is particularly undesirable for the light-transmitting end surface of the bundle directly to contact the light sensitive surface of the sensor, as such contact could result in damage, but the two surfaces must be in close parallel proximity to maintain resolution and to avoid light signal degradation.
Previous attempts to align a fiber-optic bundle accurately and to assemble the combination of the fiber-optic bundle end and sensor have resulted in a high reject rate for such assemblies, due in part to the difficulty of maintaining alignment during the assembly process, to damaging direct contact between the bundle end and the sensor during assembly, and to the choice of coupling media. Further, there has been a general failure to manufacture such assemblies which maintain the necessary light signal quality delivered to the sensor surface during normal operating conditions which may include shocks, vibrations and temperature or pressure fluctuations. Previous attempts to maintain such alignment have included transparent rigid cement and transparent fluid as coupling between the bundle and sensor. Rigid cements have failed because they do not provide adequate damping or relief of the stresses due to vibrations, temperature or pressure fluctuations, or other forces applied between the bundle and sensor. Liquid couplings have failed because of the degradation of the liquid, bubbles therein, and leaks in the liquid containment device. Further, liquid couplings do not control the proximity of the sensor and bundle surfaces. U.S. Pat. No. 4,182,545 teaches a non-permanent optical coupler system in which the coupling is of individual fibers, in contrast to the fiber-optic bundle coupled by the present invention, without use of the transparent flexible cement which results in the durability and operational permanence granted by the present invention. U.S. Pat. No. 4,790,620, although also teaching an optical coupling device, likewise does not teach the use of a transparent flexible cement for attaching a coherent fiber-optic bundle to an electro-optical sensor, discloses coupling only of an optical fiber, not a fiber-optic bundle as here, and is without the rigid guide plate of the present invention. Also, U.S. Pat. No. 4,790,620 does not teach the quality of proximity for coupling light; rather it depends upon a reflective surface added to the outer surface of the cement.
Finally there has been a rapidly expanding long felt but unfulfilled need for assemblies of fiber-optic bundles and electro-optical sensors which can be produced with a very low or non-existent reject rate, which are robust, and which maintain accuracy of operation in adverse operating conditions.